This invention relates to an apparatus for purifying contaminated air, and more particularly to a contaminated air purifying apparatus which is adapted to decrease particulates such as dust or the like floating or suspended in air, particulates such as soot or the like produced by a combustion engine, and air pollutants such as nitrogen oxides (NOx) contained in exhaust gas of a combustion engine or the like.
Conventionally, filtration using various kinds of filters has been used for removing particulates such as dust or the like which is one of air pollutants. However, the filtration often fails to catch particulates of a microscopic size depending on a filter used and tends to cause a filter used to be clogged with particulates of a rather large size.
In view of such a disadvantages, it is proposed that an electric dust collecting equipment is used in combination with or in place of a filter. A typical example of such an electric dust collecting equipment is generally constructed so as to utilize corona discharge due to application of a high voltage to particulates. More particularly, this is accomplished by electrostatically charging particulates by corona discharge due to application of a voltage as high as about 6 to 10 kV thereto and then catching the particulates by means of the electric dust collecting equipment having a voltage of about 3.3 to 6 kV.
Unfortunately, the dust collecting equipment thus constructed causes various problems due to application of a high voltage to particulates, such as generation of large unpleasant sound, production of ozone harmful to the human body and the like. Also, the dust collecting equipment exhibits another disadvantage of being large-sized because it is required to use an insulating material in a largo amount.
Further, materials which have been recently noticed as air pollutants include particulates such as soot contained in exhaust gas or the like and NOx. Removal of soot is carried out by collecting it by means of a ceramic filter or the like. Alternatively, it may be made by the above-described electric dust collecting techniques using corona discharge under a high voltage of 6 to 10 kV. However, both techniques fail to be put into practice because they cause a disadvantage of requiring additional equipment when they are applied to a small type combustion engine such as an automobile or the like. Also, they have another disadvantage of causing the equipment to be large-sized.
A decrease in concentration of NOx in exhaust gas is significantly accomplished by an ammonia catalytic reduction method or the like when production of NOx is carried out by a fixed producing source as seen in factory flue gas or the like. However, there has not been yet developed a denitration equipment effective to remove NOx produced by a moving producing source such as an automobile or the like, particularly, a diesel engine.